Tandem X-ray absorption spectroscopy and scattering forin situtime-resolved monitoring of gold nanoparticle mechanosynthesis

Current time-resolvedin situapproaches limit the scope of mechanochemical investigations possible. Here we develop a new, general approach to simultaneously follow the evolution of bulk atomic and electronic structure during a mechanochemical synthesis. This is achieved by coupling two complementary synchrotron-based X-ray methods: X-ray absorption spectroscopy (XAS) and X-ray diffraction. We apply this method to investigate the bottom-up mechanosynthesis of technologically important Au micro and nanoparticles in the presence of three different reducing agents, hydroquinone, sodium citrate, and NaBH4. Moreover, we show how XAS offers new insight into the early stage generation of growth species (e.g.monomers and clusters), which lead to the subsequent formation of nanoparticles. These processes are beyond the detection capabilities of diffraction methods. This combined X-ray approach paves the way to new directions in mechanochemical research of advanced electronic materials.Peer reviewe

Formation mechanism of a nano ring of bismuth cations and mono-lacunary Keggin-type phosphomolybdate

A new hetero-bimetallic polyoxometalate (POM) nano ring was synthesized in a one-pot procedure. The structure consists of tetrameric units containing four bismuth-substituted monolacunary Keggin anions including distorted [BiO8] cubes. The nano ring is formed via self -assembly from metal precursors in aqueous acidic medium. The compound (NH4)16[(BiPMo11O39)4]×22H2O; (P4Bi4Mo44) was characterized by single-crystal X-ray diffraction, extended X-ray absorption fine structure spectroscopy (EXAFS), Raman spectroscopy, matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF), and thermogravimetry/differential scanning calorimetry (TG-DSC-MS). The formation of the nano ring in solution was studied by time-resolved in situ small- and wide-angle X-ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo-K and the Bi-L3 edge indicating a two-step process consisting of condensation of Mo-anions and formation of Bi-Mo-units followed by a rapid self-assembly to yield the final tetrameric ring structure

Inner relaxations in equiatomic single phase high entropy cantor alloy

The superior properties of high entropy multi functional materials are strongly connected with their atomic heterogeneity through many different local atomic interactions. The detailed element specific studies on a local scale can provide insight into the primary arrangements of atoms in multicomponent systems and benefit to unravel the role of individual components in certain macroscopic properties of complex compounds. Herein, multi edge X ray absorption spectroscopy combined with reverse Monte Carlo simulations was used to explore a homogeneity of the local crystallographic ordering and specific structure relaxations of each constituent in the equiatomic single phase face centered cubic CrMnFeCoNi high entropy alloy at room temperature. Within the considered fitting approach, all five elements of the alloy were found to be distributed at the nodes of the fcc lattice without any signatures of the additional phases at the atomic scale and exhibit very close statistically averaged interatomic distances 2.54 2.55 with their nearest neighbors. Enlarged structural displacements were found solely for Cr atoms. The macroscopic magnetic properties probed by conventional magnetometry demonstrate no opening of the hysteresis loops at 5 K and illustrate a complex character of the long range magnetic order after field assisted cooling in 5 T. The observed magnetic behavior is assigned to effects related to structural relaxations of Cr. Besides, the advantages and limitations of the reverse Monte Carlo approach to studies of multicomponent systems like high entropy alloys are highlighte

Anomalies in the short range local environment and atomic diffusion in single crystalline equiatomic CrMnFeCoNi high entropy alloy

Multi edge EXAFS spectroscopy combined with reverse Monte Carlo RMC simulations was used to probe the details of element specific local coordinations and component dependent structure relaxations in single crystalline equiatomic CrMnFeCoNi high entropy alloy as a function of the annealing temperature. Two representative states, namely a high temperature state, created by annealing at 1373 K, and a low temperature state, after long term annealing at 993 K, were compared in detail. Specific features identified in atomic configurations of particular principal components indicate variations in the local environment distortions connected to different degrees of compositional disorder at the chosen representative temperatures. The detected changes provide new atomistic insights and correlate with the existence of kinks previously observed in the Arrhenius dependencies of component diffusion rates in the CrMnFeCoNi high entropy allo

Determining Structure Activity Relationships in Oxide Derived Cu Sn Catalysts During CO2 Electroreduction Using X Ray Spectroscopy

The development of earth abundant catalysts for selective electrochemical CO2 conversion is a central challenge. Cu amp; 63743;Sn bimetallic catalysts can yield selective CO2 reduction toward either CO or formate. This study presents oxide derived Cu amp; 63743;Sn catalysts tunable for either product and seeks to understand the synergetic effects between Cu and Sn causing these selectivity trends. The materials undergo significant transformations under CO2 reduction conditions, and their dynamic bulk and surface structures are revealed by correlating observations from multiple methods X ray absorption spectroscopy for in situ study, and quasi in situ X ray photoelectron spectroscopy for surface sensitivity. For both types of catalysts, Cu transforms to metallic Cu0 under reaction conditions. However, the Sn speciation and content differ significantly between the catalyst types the CO selective catalysts exhibit a surface Sn content of 13 at. predominantly present as oxidized Sn, while the formate selective catalysts display an Sn content of amp; 8776;70 at. consisting of both metallic Sn0 and Sn oxide species. Density functional theory simulations suggest that Sn amp; 948; sites weaken CO adsorption, thereby enhancing CO selectivity, while Sn0 sites hinder H adsorption and promote formate production. This study reveals the complex dependence of catalyst structure, composition, and speciation with electrochemical bias in bimetallic Cu catalyst

Recent developments of X ray absorption spectroscopy as analytical tool for biological and biomedical applications

X ray absorption spectroscopy XAS , in its various modalities, has gained exponential attention and applicability in the field of biological and biomedical systems. Particularly in this field, challenges like low concentration of analyte or proneness to radiation damage have certainly settle the basis for further analytical developments, when using X ray based methods. Low concentration calls for higher sensitivity by increasing the detection limits DL ; while susceptibility for radiation damage requires shorter measurement times and or cryogenic sample environment possibilities. This manuscript reviews the latest analytical possibilities that make XAS more and more adequate to investigate biological or biomedical systems in the last 5 amp; 8201;year

Increasing the Efficiency of Optimized V SBA 15 Catalysts in the Selective Oxidation of Methane to Formaldehyde by Artificial Neural Network Modelling

The present study investigates the possibility of improving the selective oxidation of methane to formaldehyde over V SBA 15 catalysts in two different ways. In a classical approach of catalyst optimization, the in situ synthesis of V SBA 15 catalysts was optimized with regard to the applied pH value. Among the set of catalysts synthesized, a higher amount of incorporated vanadium, a higher content of polymeric VOx species as well as a less ordered structure of the support material were observed by increasing the pH values from 2.0 to 3.0. An optimum in performance during the selective oxidation of methane to formaldehyde with respect to activity and selectivity was found over V SBA 15 prepared at a pH value of 2.5. With this knowledge, we have now evaluated the possibilities of reaction control using this catalyst. Specifically, artificial neural network modelling was applied after the collection of 232 training samples for obtaining insight into the influence of different reaction parameters temperature; gas hourly space velocity GHSV ; and concentration of O2, N2 and H2O onto methane conversion and selectivity towards formaldehyde. This optimization of reaction conditions resulted in an outstanding high space time yield of 13.6 kgCH2O amp; 8729;kgcat amp; 8729;h amp; 8722;

Estudo tecnol gico e composicional da folha de ouro de ret bulos barrocos bases para uma metodologia de investiga o

The gold leaf from one of the most important art works of the Portuguese Baroque period, the main altarpiece of the Church of Jesus in Aveiro, currently part of the city Museum and former Convent of Jesus, was studied. Qualitative analysis of the samples cross-section was performed by optical microscopy. Three different layers – ground layer, bole and gold – were identified, a result consistent with a traditional gilding. The use of scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) showed the use of a ternary Au-Ag-Cu alloy, with approximately 22 carats. Through inductively coupled plasma mass spectrometry (ICP-MS) it was possible to identify trace elements such as Cr, Pt, Pd and Sn in the gold, and Pb and Hg in the bole layer. The use of synchrotron radiation micro X-ray fluorescence (SR-µXRF) confirmed the presence of Sn and allowed to establish a profile of the main elements in the samples